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    <title>Document</title>
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    <script>
        
        /*
        5! = 5*4*3*2*1
        */


        function fn(num) {
            if(num === 1) {
                return 1;
            }
            return num * fn(num - 1);
        }
        var sum = fn(5);
        console.log(sum)
    </script>
</body>
</html>